Atomic Absorption Spectrometry Question

Biodegradable

When testing for element composition, why don't they use white light as the source of radiation in atomic absorption spectrometry? As in, why don't they pass the white light through gaseous form of a sample before going through a prism to give the spectrum? Instead they use a light source that emits the characteristic light from the element being tested for, along with a flame.

Let's say they're testing for sodium. Am I right to say that they're in effect using the light that would go on to form an emission line spectrum unique to sodium? And I'm also curious as to what effect the naked flame (with no sample being burned) has on the light transmitted through it and on the resulting emission line spectrum in comparison to if there were no flame? So I presume that the more of the element that is in the sample being burned, the less intense the line spectrum will be.

mistress_gi

If the measurement absorption then you shine the correct wavelength through (ie. light of the wavelength that is optimily absorber) and "check" how much is absorbed.
What you describing is an emission profile.
In fact this is what is used to determine the absorption profile and then you can use that to determine, for example, the concentration of that substance in, say, a mixture.
I hope that makes sense!